Effect of Radiation Models on Coal Gasification Simulation

2012 ◽  
Author(s):  
Xijia Lu ◽  
Ting Wang
Keyword(s):  
Wall Temperature ◽  
Coal Gasification ◽  
Cfd Simulation ◽  
Stokes Equations ◽  
Heterogeneous Reactions ◽  
Coal Slurry ◽  
Radiation Model ◽  
Entrained Flow ◽  
Gasification Process ◽  
Coal Particles

Adequate modeling of radiation heat transfer is important in CFD simulation of coal gasification process. In an entrained-flow gasifer, the non-participating effect of coal particles, soot, ashes, and reactive gases could significantly affect the temperature distribution in the gasifier and hence affects the local reaction rate and life expectancy of wall materials. For slagging type gasifiers, radiation further affects the forming process of corrosive slag on the wall which can expedite degradation of the refractory lining in the gasifier. For these reasons, this paper focuses on investigating applications of five different radiation models to coal gasification process, including Discrete Transfer Radiation Model (DTRM), P-1 Radiation Model, Rosseland Radiation Model, Surface-to-Surface (S2S) Radiation Model, and Discrete Ordinates (DO) Radiation Model. The objective is to identify the pros and cons of each model’s applicability to the gasification process and determine which radiation model is most appropriate for simulating the process in entrained-flow gasifiers. The Eulerian-Lagrangian approach is applied to solve the Navier-Stokes equations, nine species transport equations, and seven global reactions consisting of three heterogeneous reactions and four homogeneous reactions. The coal particles are tracked with the Lagrangian method. Six cases are studied—one without the radiation model and the other five with different radiation models. The result reveals that the various radiation models yield uncomfortably large uncertainties in predicting syngas composition, syngas temperature, and wall temperature. The Rosseland model does not yield reasonable and realistic results for gasification process. The DTRM model predicts very high syngas and wall temperatures in the dry coal feed case. In the one-stage coal slurry case, DTRM result is close to the S2S result. The P1 method seems to behave stably and is robust in predicting the syngas temperature and composition; it yields the result most close to the mean, but it seems to underpredict the gasifier’s inner wall temperature.

scholarly journals Investigation of the Coal Gasification Process Under Various Operating Conditions Inside a Two-Stage Entrained Flow Gasifier

2012 ◽  
Vol 4 (2) ◽  
Author(s):  
Armin Silaen ◽  
Ting Wang
Keyword(s):  
Coal Gasification ◽  
Operating Conditions ◽  
Coal Slurry ◽  
Two Stage ◽  
Heating Value ◽  
Fuel Distribution ◽  
Entrained Flow ◽  
One Stage ◽  
Gasification Process ◽  
Entrained Flow Gasifier

Numerical simulations of the coal gasification process inside a generic 2-stage entrained-flow gasifier fed with Indonesian coal at approximately 2000 metric ton/day are carried out. The 3D Navier–Stokes equations and eight species transport equations are solved with three heterogeneous global reactions, three homogeneous reactions, and two-step thermal cracking equation of volatiles. The chemical percolation devolatilization (CPD) model is used for the devolatilization process. This study is conducted to investigate the effects of different operation parameters on the gasification process including coal mixture (dry versus slurry), oxidant (oxygen-blown versus air-blown), and different coal distribution between two stages. In the two-stage coal-slurry feed operation, the dominant reactions are intense char combustion in the first stage and enhanced gasification reactions in the second stage. The gas temperature in the first stage for the dry-fed case is about 800 K higher than the slurry-fed case. This calls for attention of additional refractory maintenance in the dry-fed case. One-stage operation yields higher H2, CO and CH4 combined than if a two-stage operation is used, but with a lower syngas heating value. The higher heating value (HHV) of syngas for the one-stage operation is 7.68 MJ/kg, compared with 8.24 MJ/kg for two-stage operation with 75%–25% fuel distribution and 9.03 MJ/kg for two-stage operation with 50%–50% fuel distribution. Carbon conversion efficiency of the air-blown case is 77.3%, which is much lower than that of the oxygen-blown case (99.4%). The syngas heating value for the air-blown case is 4.40 MJ/kg, which is almost half of the heating value of the oxygen-blown case (8.24 MJ/kg).

Prediction and Validation of Performance of an Entrained Flow Gasifier Model

2011 ◽  
Author(s):  
Arnab Roy ◽  
Srinath V. Ekkad ◽  
Uri Vandsburger
Keyword(s):  
Particle Deposition ◽  
Cfd Simulation ◽  
Particle Surface ◽  
Model Parameters ◽  
Discrete Phase Model ◽  
Improve Design ◽  
Entrained Flow ◽  
Gasification Process ◽  
Coal Particles ◽  
Entrained Flow Gasifier

Computational fluid dynamics (CFD) simulation of a single stage, dry-feed entrained flow gasifier is carried out to predict several physical and chemical processes within the gasifier. The model is developed using a commercial software package FLUENT. The CFD model is based on an Eulerian-Lagrangian framework, where the continuous fluid phase is modeled in Eulerian approach and the particle flow trajectory is simulated in Lagrangian frame. The two phases are coupled by appropriate source terms in the conservation equations. The gasification process can be divided into the following sub-processes, which are inert heating, moisture release, coal devolatilization, char gasification and gas phase reactions. Discrete Phase Model (DPM) is used to model the coal particles and coupled with heterogeneous particle surface reactions in Species Transport module. The interaction between reaction chemistry and turbulence is described by Finite-rate/Eddy dissipation model. The simulation provides detailed information of temperature field and species concentration profile inside the gasifier. The temperature distribution clearly indicates the three different reaction zones for devolatilization, gasification and reduction. Steady state model predictions are compared with benchmark experimental data from literature. The trend of the predicted species mole fraction distribution is in good agreement within error bound of the experiment. The model thus provides a validated set of model parameters along with an insight to the underlying flow physics and chemical reactions of gasification process that can be employed to improve design of experiments. This study also develops the basis to achieve further accuracy incorporating complex effects such as detailed reaction kinetic mechanisms, proper devolatilization models, effect of ash-slag transition and particle deposition.

Design and Simulation of a Hybrid Entrained-Flow and Fluidized Bed Mild Gasifier: Part 1—Design Considerations and Development of a Multiphase Model

2011 ◽  
Author(s):  
A. K. M. Monayem Mazumder ◽  
Ting Wang ◽  
Jobaidur R. Khan
Keyword(s):  
Power Plant ◽  
Computational Model ◽  
Fluidized Bed ◽  
Stokes Equations ◽  
High Energy ◽  
Multiphase Model ◽  
Entrained Flow ◽  
Design Considerations ◽  
Gasification Process ◽  
Coal Particles

A mild gasification process has been developed to provide an innovative form of clean coal technology, which can be utilized to build a new, highly efficient, and compact power plant or to retrofit an existing coal-fired power plant in order to achieve lower emissions and significantly improved thermal efficiency. The core technology of the mild gasification power plant lies on the design of a compact and effective mild gasifier that can produce synthesis gases with high energy volatiles through a hybrid system: utilizing the features of both entrained-flow and fluidized bed gasifiers. The objectives of this study are to (a) describe the features and design considerations of this mild gasifier and (b) develop a multiphase computational model to guide the design of the mild-gasifier by investigating the thermal-flow and gasification process inside a conceptual mild gasifier. Due to the involvement of a fluidized bed, the Eulerian-Eulerian method is employed to calculate both the primary phase (air) and the secondary phase (coal particles). Multiphase constitutive equations developed from kinetic theory are employed for calculating the effective shear viscosities, bulk viscosities, and effective thermal conductivities of granular flows to simulate the hydrodynamic and thermal interactions between the solid and gas phases. Multiphase Nativer-Stokes equations and seven global reaction equations with associated species transported equations are implementd to simulate the mild gasification process. Part 1 of this paper documents the design principle of the mild gasifier as well as the development of the computational model starting from single phase, then using multiple phases, and finally including all reactions in the multiphase flow.

A Multiphase Eulerian-Eulerian CFD Simulation of Fluidized Bed Gasification Using Malaysian Low-Rank Coal-Merit Pila

2017 ◽  
Vol 740 ◽  
pp. 163-172 ◽  
Author(s):  
Kamariah Md Isa ◽  
Kahar Osman ◽  
Nor Fadzilah Othman ◽  
Nik Rosli Abdullah ◽  
Mohd Norhakem Hamid
Keyword(s):  
Coal Gasification ◽  
Cfd Simulation ◽  
Heterogeneous Reactions ◽  
Low Rank ◽  
Maximum Temperature ◽  
Low Rank Coal ◽  
Gasification Process ◽  
Granular Particle ◽  
Experimental Values ◽  
Good Agreement

A multiphase Eulerian- eulerian model integrating the kinetic theory of granular particle (KTGF) was used to simulate the gasification of Malaysian low- rank coal (LRC), Merit- Pila inside a bubbling fluidised bed (BFB) gasifier. The model used includes the bubbling phenomenon and gasificationprocess that occurs inside a BFB gasifier. The gasification process simulated includes drying, heterogeneous reactions of char combustion, devolatilization, water- gas shift reaction, Boudourd reactionand gas phase homogenous reactions. The results from this model are compared to the results of Merit-Pila coal gasification, from which experimental data is available. Comparison of the pressure profile shows good agreement with experimental results. The temperature distribution shows that the maximum temperature is around 1100K which also shows good agreement with experimental values which is 1087K. Besides that, three out of six species mass fraction which is N2, H2 and CH4 produced similar values with experimental values. This shows the simulation conducted was capable to predict the gasification process of Low- rank coal, namely Merit-Pila.

Design and Simulation of a Hybrid Entrained-Flow and Fluidized Bed Mild Gasifier: Part 2—Case Study and Analysis

2011 ◽  
Author(s):  
A. K. M. Monayem Mazumder ◽  
Ting Wang ◽  
Jobaidur R. Khan
Keyword(s):  
Multiphase Flow ◽  
Fluidized Bed ◽  
Flow Behavior ◽  
Flame Temperature ◽  
Heterogeneous Reactions ◽  
Thermal Flow ◽  
Entrained Flow ◽  
Progressive Development ◽  
Gasification Process ◽  
Flow And Heat Transfer

To help design a mild-gasifier, a reactive multiphase flow computational model has been developed in Part 1 using Eulerian-Eulerian method to investigate the thermal-flow and gasification process inside a conceptual, hybrid entrained-flow and fluidized-bed mild-gasifier. In Part 2, the results of the verifications and the progressive development from simple conditions without particles and reactions to complicated conditions with full reactive multiphase flow are presented. Development of the model starts from simulating single-phase turbulent flow and heat transfer in order to understand the thermal-flow behavior, followed by introducing seven global, homogeneous gasification reactions progressively added one equation at a time. Finally, the particles are introduced, and heterogeneous reactions are added in a granular flow field. The mass-weighted, adiabatic flame temperature is validated through theoretical calculation and the minimum fluidization velocity is found to be close to Ergun’s correlation. Furthermore, the predicted exit species composition is consistent with the equilibrium values.

Effect of Swirl on Gasification Characteristics in an Entrained-flow Coal Gasifier

2020 ◽  
Vol 18 (3) ◽  
Author(s):  
Rongbin Li ◽  
Mingzhuang Xie ◽  
Hui Jin ◽  
Liejin Guo ◽  
Fengqin Liu
Keyword(s):  
Coal Gasification ◽  
Three Dimensional ◽  
Reaction Model ◽  
Gas Temperature ◽  
Swirl Number ◽  
Entrained Flow ◽  
Gasification Process ◽  
Cold Gas Efficiency ◽  
Product Composition ◽  
Gas Efficiency

AbstractThe three-dimensional (3-D) comprehensive mathematical model was developed to simulate the coal gasification process in an entrained flow gasifier with a swirl burner. The models employed or developed includes the coal devolatilization model, the char combustion and gasification model, the gas homogeneous reaction model, the random-trajectory model, gas turbulence model, and the P-1 radiation model. The solution of models was executed based on the computational fluid dynamics (CFD). By qualitatively comparing the results at different swirl number, the significant influences of swirl on characteristics of coal gasification such as flow distributions, gas temperature and product composition including hydrogen (H2), carbon monoxide (CO), etc., and on the performance of coal gasification such as averaged exit product composition, carbon conversion rate and cold gas efficiency, were in detail discussed. Especially, a proper swirl number (S ≤ 0.65) in favor of gasification was found for the investigated gasifier in this paper.

scholarly journals Pulverized coal gasification with steam and flue gas

2018 ◽  
Vol 240 ◽  
pp. 05036
Author(s):  
Robert Zarzycki
Keyword(s):  
Coal Gasification ◽  
Flow Reactor ◽  
Coal Dust ◽  
Pulverized Coal ◽  
Numerical Calculations ◽  
Fuel Oil ◽  
Eddy Motion ◽  
Entrained Flow ◽  
Gasification Process ◽  
Entrained Flow Reactor

The study presents the concept and numerical calculations of the coal dust gasification in the entrained flow reactor with power of 16 MWt. The gasification process in the reactor can be performed in the atmosphere of O2, CO2 and H2O. The combustible gases obtained during gasification are composed mainly of CO and H2 and can be used to feed pulverized coal-fired boilers. Integration of the reactor (reactors) for coal dust gasification with the pulverized coal-fired boiler allows for improved flexibility, especially in the range of low loads if stabilization of coal dust combustion in pulverized-fuel burners or support for their work with ignition burners fed with gas or light fuel oil is necessary. The concept of the gasification reactor assumes strong eddy motion of the coal dust, which substantially allows for elongation of the time of fuel remaining in the reactor and obtaining a high reaction level. The concept of the entrained flow reactor presented in this study and the results of numerical calculations can be helpful for development of the devices with greater powers which in the nearest future should be integrated in the systems of pulverized coal-fired boilers in order to reduce their minimum load without using the ignition burners.

CFD simulation of entrained-flow coal gasification: Coal particle density/sizefraction effects

2010 ◽  
Vol 203 (1) ◽  
pp. 98-108 ◽  
Author(s):  
Andrew Slezak ◽  
John M. Kuhlman ◽  
Lawrence J. Shadle ◽  
James Spenik ◽  
Shaoping Shi
Keyword(s):  
Coal Particle ◽  
Coal Gasification ◽  
Cfd Simulation ◽  
Particle Density ◽  
Entrained Flow

scholarly journals A Modified Gibbs Free Energy Minimisation Model for Fluid Bed Coal Gasification

2015 ◽  
Vol 36 (1) ◽  
pp. 73-87 ◽  
Author(s):  
Marek Ściążko ◽  
Leszek Stępień
Keyword(s):  
Large Scale ◽  
Coal Gasification ◽  
Heterogeneous Reactions ◽  
Boudouard Reaction ◽  
Quasi Equilibrium ◽  
Gaseous Species ◽  
Gasification Process ◽  
Energy Minimisation ◽  
Inorganic Matter ◽  
Fluid Bed

Abstract A modified approach to equilibrium modelling of coal gasification is presented, based on global thermodynamic analysis of both homogeneous and heterogeneous reactions occurring during a gasification process conducted in a circulating fluid bed reactor. The model is based on large-scale experiments (ca. 200 kg/h) with air used as a gasification agent and introduces empirical modifications governing the quasi-equilibrium state of two reactions: water-gas shift and Boudouard reaction. The model predicts the formation of the eight key gaseous species: CO, CO2, H2O, H2, H2S, N2, COS and CH4, volatile hydrocarbons represented by propane and benzene, tar represented by naphthalene, and char containing the five elements C, H, O, N, S and inorganic matter.

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